Wenjay Sung, DPM discusses the basics for ordering and interpreting laboratory blood tests. Dr Sung also discusses the importance for each test, how they are obtained, and what clinical value each test may provide for a patient.
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TAPE STARTS – [00:00]
Male Speaker: Okay, our next speaker is new to our group, Wenjay Sung, comes to us from Southern California. He was a past resident at the University of Pittsburgh Medical Center and our fellow here at Weil. And on the theme of medical management of our patients, he’s going to be doing a review of laboratory values. I think this is very important for us also.
Let’s welcome Dr. Jay Sung.
Okay, got it.
Wenjay Sung: All right. Thanks again, present. Thank you, Dr. Bob Freiburg.
So we’re going to review our laboratory values. We want to do this right before the residency rumble. So hopefully, you residents are taking notes or anybody who’s about to take their boards, this is a good review.
So I have no disclosures for this presentation. Let’s know the basic values of what the laboratory values are for and we’re just going to go over some of the basics. So laboratory values are given in ranges, be as many labs just have different interpretations of reference ranges. They’re roughly the same. However, most of them from thousands or sometimes hundreds of labs and then they all come up with a range of what they think is acceptable. Most of them are about the same.
So I’m going to give you a reference range usually from Medline. The reference range is usually set about a value of 95% of normal population. So whatever that population, whether you’re from New York or Southern California, that’s actually where they’re bringing their data from. So it’s actually the localized data as well. Data from the US may be a little different from data, say, from China. It’s just really from a localized lab and that’s how they’re going to get their reference ranges. Most values are based on the concentration in the blood plasma and we’re going to get into that.
So what is blood plasma? Well, blood plasma is a yellowish-colored liquid. It’s part of the blood that normally holds the blood cells. It’s not actually the blood cells itself. It’s actually what the liquid part that holds the blood cells in suspension.
This makes the plasma the extracellular matrix of blood cells. It makes about 55% of the total body’s volume and intervascular fluid part of the extracellular fluid. It’s mostly water, of course, and we’re mostly water. It’s dissolved proteins, glucose, clotting factors, electrolytes hormones, carbon dioxide, and oxygen.
What’s important is that laboratory values are based on the concentration, again, in blood plasma. That’s not – it’s not the oxygen-based. It’s not something in your cells. It’s actually in the plasma itself.
So the nuances of three very most common popular ordered blood test, the CBC, the BNP, and the CMP.
So the CBC is a complete blood count with or without differentiation. We’ll talk about that. It’s usually drawn from the venous, peripheral venous blood usually collected in the laboratory, too. An unacceptable specimen is something that’s been clotted or something that’s been sitting around for over 48 hours that you won’t be able to use that. Usually, they use a whole blood analyzer in order to test the blood and generally patients can get this 24 hours a day, seven days a week at all time. So you can literally get the blood test every 10 minutes if you wanted to. However, that obviously would be bad for your patients and bad patient care. And we’ll talk more about that in a second.
What is measured in the CBC? Well, the red blood cell data, the white blood cell data, and the platelet count. Now, when we talk about white – red blood cell data, there’s a lot of different things within the red blood cell data including hemoglobin, hematocrit, mean corpuscular volume. The red blood cell distribution width and we’ll talk about why that’s important. Why blood cell data? Obviously, we want the leukocyte count and also to differential may be ordered in order to see if they’re – like I’m sure you’ve heard of white shift, left shift, whether it is infected or not and we’ll discuss that as well.
So total red blood cell count and that’s kind of the number of circulating red blood cells in the one microliter of peripheral venous blood. But generally, for females, it’s about 4.2 to 5.4. In males, it’s about 4.7 to 6.1.
I’m not sure if this mnemonic actually helped. I literally just got this from a nursing book. So I’m not sure if this actually works or not because I didn’t use that when I was starting the training for this. But you can take that for what it’s worth. And by the way, you guys are going to have all a copy of my lecture afterwards, there’s no – I’m not keeping any of these. These are all free for anybody who wants to download them off the internet. So you don’t need to write any of this down. But I’m not sure if this mnemonic works or not.
The hemoglobin. The hemoglobin concentration is the amount of hemoglobin in the peripheral blood. It’s usually the reflection of the number of blood cells in the blood and it’s over 90% of the red blood cell. So a decrease in hemoglobin can mean a couple of things. It can mean anemia. And an increase in hemoglobin can mean polycythemia. For females, generally, it’s about 12 and 16. And there’s a difference between males and females obviously. And I mean, 12 and 16 is for females. For males, it’s about 14 to 18. So just a little more when it comes to the males. And again, there’s mnemonics on the bottom if anybody cares.
Hematocrit is a little different story and you tend to see it on an H&H. Hematocrit is the measure of the blood – percentage of the total blood volume that’s made up by red blood cells. What does that mean? That means if we spin in a centrifuge and you see the actual percentage of hematocrit, you’d actually see the amount of cell – red blood cells versus the amount of plasma. What does that mean? That means literally, in a centrifuge, you mix the blood, and then after a certain time, you measure the percentage of red blood cells versus the rest, and in normal male adults, it’s about 40 to 54; females, about 34 to 51.
And this case, what’s it look like after you centrifuge it, well, looks like there’s anemia because there’s a low red blood cell percentage, low hematocrit.
There might be some anemia going on.
Obviously we don’t do that all time, it’s quite impractical. So it’s usually calculated from the RBCs and also from the muscular corporal volume, and so there’s usually a formula in order to actually calculate rather than spinning it down, but sometimes you can order an actual spin for the hematocrit.
So again, hematocrit is different values for male and female and here’s a little mnemonic for it. He may have 42% to 54% of his toes, but she criticizes him 35% to 40% of the time. I’m not sure how that’s mnemonic, but it’s, well.
Mean corpuscular value volume against the measure of the average volume or size of a red blood cell, and it’s determined by this. Determined by the number of the cells and the actual, the volume of it, and they take it from the histogram, and measure the mean volume, just like regular geometry, this can be a math class.
And the results usually, I’m not sure if you can read this. So the importance of MCV is actually classified in the times of anemia, whether it’s a normocytic anemia, a microcytic anemia, or macrocytic anemia. So when it comes to describing the classifications of anemia, getting this value can give you the types of anemia that could be, and this is the normal value, usually between 80 to 100 microliters.
We get another example of, let’s consider it a microcytic red blood cells and macrocytic blood cells. So red blood cell distribution with, exactly what it sounds like, it’s the indication and variation of the size of the red blood cell.
It’s usually derived from the histogram and also represents the coefficient of the variation of the curve. So if we look in general, the red blood cell distribution width is usually between 11 to 14, 11.5 to 14, and with this size, anemias are usually associated, especially if it’s a deviation from the norm, such as a vitamin B12 deficiency, iron, and folate deficiencies.
So thalassemia is a very common microcytic anemia that’s usually characteristic of an abnormal red blood cell distribution width. So it’s something to keep in mind when also doing pathology.
White blood cell count, I think we’re more familiar with this, especially when it comes to infection, so it has to do a lot of wound care. The total white blood cell count or the leukocyte count in one microliter of blood usually decrease in number, could mean leukopenia. Increase in number of blood can mean leukocytosis or it could be an infection. Now, white blood cell count, this is what the typical range is, depending on where you are, but it’s usually 5,000 to 10,000.
When a differentiation is ordered, the percentage of E-type of leukocyte is then brought out. So each type of leukocytes could be neutrophils, lymphocytes, monocytes, eosinophils, and basophils. So this is when we start breaking up the different types of white blood cells when it counts for a differential.
And it’s usually for manually or automated. So when you do a manual differentiation, usually you have somebody who actually goes in there, and reads it, and then counts it out based on 100. Obviously it’ll take a lot more effort to do something like this.
I think now we are most – the standard care is actually to get it automated because this actually cost a lot of money to do a manual differentiating. Automated again is just performed by an instrument and also performed more by machine that actually counts it for you.
Platelet count, the number of platelets per cubic milliliter of blood, usually decreases thrombocytopenia and increases thrombocytosis, and the range usually is 150 to 400. [10:09] This is a shorthand, I’m sure a lot of the residents out there already know how to write this.
It’s how usually we’ll see it and which is what represents. So BMP, the BMP, now we’re going to basic metabolic panel. BMP is usually grouped as a single profile, usually is called a CHEM-7, that’s what it’s usually called. And so test some of the electrolytes of kidney functions. So sodium potassium, chloride, a lot of these are based on how the kidney will function. So when people order this, not only does it affect most of the body, but the kidneys kind of show the reflection of what’s going on in the body. So that’s what the order of BMP.
So with the BMP, just some of the little details, peripheral blood can be collected in three types of vials, usually a light green, that’s associated with the plasma reporting or what’s in anticoagulant, a gold and a red, usually a serum, and the red one has no additives added.
Again, same thing that can be ordered seven days a week, 24/7 at all times. And so the average value for sodium, well for sodium it’s a major catatonic, excuse me, cation in the extracellular space. Generally, it’s about 140, if you remember that. And it’s a major determinant of extracellular osmolarity. Increase of sodium levels is usually hypernatremia and a decrease is hyponatremia. This is what the usual range is about 140, 136 to 145. She swims in the ocean, drink salt water or 136 minutes to 145 minutes.
Potassium, it’s a major intracellular cation with the level of four, usually four by the serum. Elevated serum potassium levels can mean a hyperkalemia, and of course, a decrease is hypokalemia.
Sometimes it can be falsely elevated, generally there’s – a reason is, you know, with the red blood cell being lysed during simple phlebotomy, sometimes the potassium is released in the serum, resulting in an elevated – false elevation. So potassium, she eats about 3.5 bananas and – yeah. So 3.5 to 5, that’s usually what the normal potassium is.
Chloride, generally, it’s another major extracellular anion, instead of a cation. They’re really, really rare to actually have a – you know isolated hyperchloremia or hypochloremia. I’m not used to saying to those words, because we never really hear about them, it’s very rare that we actually ever have to deal with them. Generally, again, it’s dealing with the kidneys. Usually, it’s a part of a larger shift with their – if there’s something else going on with the sodium or bicarbonate. But, you know, the normal range is between 98 to 106.
Carbon dioxide count. So usually, it’s measured as a bicarbonate ion that exists within the serum, so the carbon dioxide count. And most often referred to as, you know, the bicarbonate level when we talk about carbon dioxide content. So the carbon dioxide content is generally between 23 and 30. So the pneumonic is Carly is 23 and goes to Dickson’s 30/30 party.
Blood urea and nitrogen. Well, BNU measures the amount of urinary nitrogen in the blood. And urea is formed in the liver, the end by-product protein and is transported, of course, through the kidneys for excretion. So nearly all renal diseases can cause an inadequate excretion of BUN. So if that rises above normal or lowers, there’s usually something wrong with the kidneys.
It’s also very important to also look at the creatinine test, because that also usually – that goes into conjunction if there’s kidney – renal function studies. So blood urea and nitrogen, between 10 and 12 milligrams per deciliter. Pneumonic, I wish I can eat 10 to 12 buns. That was not bad, yeah.
Creatinine. It usually measures the amount of creatinine in the blood, obviously. It’s a catabolic by-product of a creatine phosphatase. And usually, it measures a skeletal contraction or skeletal muscle lysis. People who tend to have heart attacks tend to have a higher level of creatinine as well. Creatinine as well as blood urine nitrogen is usually excreted entirely through the kidneys and therefore, excellent measures of renal function.
So we see right here, it’s between 0.6 to 1.2. And creatinine is, again, the by-product of a creatine phosphatase, and it usually get excreted through the kidneys exclusively.
So glucose, you know, evaluation to – again, this is kind of tricky because, again, when the patient’s glucose rises and falls, it’s usually the most common and the most popular type of test for patients, because it could be in relation to their meal, whether they ate a meal, whether they’re fasting. So glucose can rise and fall within a few – a few hours.
So postprandial versus fasting, all the glucose level obviously could be indicative of diabetes mellitus. And glucose is the most commonly measured laboratory test. Usually, what we consider normal, between 70 and 110 milligrams of – milligrams over deciliter.
For the board – for those who are taking boards and those who are taking review exams, so forth, understand this is going to – this is no longer how we diagnose diabetes, now we use an A1C measure. But if you’re taking the test, this is what they’re going to have.
The criteria for diagnosing diabetes is fasting glucose must be greater than 120 milligrams over deciliter, two hours postpartum glucose is over 200, and the random plasma glucose is over 200. So that is actually the board answer, all right. Because now we – I know we changed to A1C level based on how they are over the three months period, but when it comes to boards, that’s what you need to remember. If you still remember that from school, that’s still correct today.
Total calcium. Calcium, again, is just a measure of free ionized calcium and serum blood. It’s usually bound to albumin, which is a protein in the blood. Therefore, it can be changed. Those calcium actually can be altered and can be varied based on the amount of albumin or based on the amount of protein in your blood. But calcium is between 9 and 10.5. She drinks 9 to 10.5 ounces of milk. I guess that, these used to come in 10.5 ounces of milk before. I’m not sure.
So one final BMP per, again, this is how it’s usually written out. That’s what it usually looks like.
So complete metabolic panel, I’m not going to go over everything again, obviously. This is a more extensive laboratory and usually evaluates more organ dysfunction, including protein, and we’ll talk about more – about some of the protein counts to albumin – and total protein is usually albumin, and globulin protein is measured in the total blood test. It usually ranges about 10 – excuse me, 60 to 80 albumin.
I’m just going to go over these really quick. Albumin consists of 60% total protein within the extracellular portion of the blood. And hemoglobin, obviously, is the most abundant protein. It has a major effect within the blood pressure, and also can transport blood – constitutes – so the amount of albumin in the body can affect the amount of hormones, enzymes, and drugs being delivered through the blood streams of a – if you have low albumin count, such the protein count.
If you try to introduce antibiotics or any other drugs, a low albumin can affect the actual delivery of the drug as well. Albumin is therefore, synthesized in the liver, and it’s also a measure of hepatic function. This is a normal 35 to 50 grams.
Alkaline phosphatase is usually an enzyme present with a number of tissues, including liver, bone, kidneys, intestines, so it’s all over the place. It’s great because, again, it’s a form of enzyme that does measure the callus of same reactions but in different structures of the body, and it’s between a 50 and 100. Obviously, we usually – when you look at this, you think it’s more of a liver test, and that’s what we tend to use it for. We actually get a liver panel, when prescribed to bonafide and so forth, but again, it does affect all – it does have the same type of reaction for a lot of different organs in the body.
Bilirubin, the sum of conjugated and unconjugated bilirubin, so it’s not just one type. It’s usually unconjugated mix of blood, 50% to 85%. Remember that bilirubin metabolism begins with the breakdown of red blood cells. So if you start seeing a high level of bilirubin, there’s a red blood cell destruction in the body. Yeah, it’s usually between 2 to 20.
Again, AST, this is another – something that we do measure when it comes to a liver function test. Usually present in both the cardiac and liver muscles, but again, most of us I think, use this for more of a LFT type of test. It’s usually inflection of some type of hepatocellular injury, but again, it could be a heart or skeletal muscle injury. Between a 5 and a 30.
So when you do order a CMP test, this is what we typically get. Now, just looking at this – this is kind of like what the residency rumble is going to be, you’re going to get a bunch of tests, a bunch of labs like this, and some may be high, some may be low.
Looking at this, what do you think is going on with that patient? A history of congestive heart failure? Again, there’s other labs, but just looking at the CMP, what would you suggest?
Again, you’re all going to get a copy of this, so no need to take pictures. So, the interpretation of that. So if you look at the BMP and creatinine, it’s usually consistent with azotemia, so we have the BNU and creatinine. It’s over 20 to 1, so the result, inadequate renal perfusion, so there’s definitely some renal issues going on. Not just congestive heart failure but you have some pressure on the kidneys. That’s typical.
Now you also have hepatic congestion, all right. When you start getting the hepatic congestion, you’re getting some hypoxia and dead liver cells as well, not just from the congestive heart failure. But bilirubin, we looked at that, that was also increased, and total protein decline – low. When you’re declining total protein, it’s also – it means a decrease albumin in the liver, so you’re getting some hepatic damage, hepatic pathology as well from the congestive heart failure.
So another thing that’s changing is you see there’s definitely some hyponatremia. Again, it’s definitely some results going on with the kidneys, and hyperglycemia. Because it’s not really that high, we look at 1.12 – I’m sure a lot of our patients, 1.12 is a good thing. In this case, it’s not really something that – whether it’s – it depends one when it was taken. Obviously, they’re not trying to measure for diabetes at this time, so whether it’s fasting or random sample, that’s not as important. So that was kind of a, you know, a lame duck there.
So final comments. I mentioned earlier that we can or do labs anytime, 24 hours, seven days a week. Obviously, we don’t want to do that because you can cause an iatrogenic anemia, but please don’t do that. Blood test is, again, to be helpful for the patients and to interpret and to learn what’s going on with the patient. It’s kind of our detective work when we order what’s going on. We need to find the evidence of what’s going on and lab work is supposed to help us with that. No laboratory test should ever, ever be ordered unless medically necessary.
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